1. Field of the Invention
The present invention generally relates to coverings for splice connections in electrical cables, and more particularly to a transition joint for use when splicing or terminating a cable having an oil-impregnated layer.
2. Description of the Prior Art
Electrical cables, such as those used for telephone lines, high voltage lines, cable television, etc., can develop faults or breaks in the line due to manufacturing defects or environmental factors. Faults occur both in underground and aerial cables. Rather than replacing an entire section of such a cable, it is expedient to expose a portion of cable, repair the fault, and place an enclosure about the connection. Splicing of electrical wires is similarly useful in the connection of successive cable sections, and in the termination of such cables.
One of the earliest constructions for these cables, particularly for underground telephone and power cables, consists of a lead jacket surrounding one or more conductors, with a layer of insulative, oil-impregnated paper placed between the lead jacket and the conductors. Although modern underground cables now have extruded dielectric (plastic) jackets, with no fluid inside, there are still substantial amounts of the paper-insulated lead cables ("PILC") in use. A problem thus arises when a PILC cable needs to be repaired or terminated, due to the deleterious effects caused by the egress of the oil or other dielectric fluid.
Several prior art patents are directed to splicing of PILC cables, including U.S. Pat. Nos. 4,110,550 issued to Di Pietro; 4,354,050 issued to Gregory; 4,375,577 issued to Silver et al.; 4,383,131 issued to Clabburn; 4,638,112 issued to Giorgio et al.; and 4,695,676 issued to Lawrence et al. Each of these patents, however, suffer from certain drawbacks. For example, in the transition splice disclosed in Clabburn (see FIG. 4), four separate layers of polymeric materials are used in addition to an internal void filling material and an outer metallic braid. Clearly, this construction is unduly complicated and requires an excessive amount of time to assemble. Those skilled in the art will further appreciate that the Clabburn construction, while disclosing the use of elastomeric tubing, requires that an oil-impervious layer be interposed between any such elastomeric tubing and the oil-impregnated paper. Such an oil-impervious layer has been required in prior art splice assemblies due to the fact that, if the oil comes into direct contact with the elastomeric layer, the oil will be absorbed into the elastomer, causing it to swell and eventually degrade; this promotes the creation of voids at the interface between the elastomer and the cable, leading to high-voltage failures. Finally, Clabburn relies on a heat shrinkable material which is in contact with the cable; this construction is undesirable since, as the material is heated, oil within the cable can easily vaporize and leave a harmful void between the cable surface and the oil-impervious (heat shrinkable) layer.
The Di Pietro, Gregory, Silver et al. and Giorgio et al. assemblies each require several metallic parts, such as bars, ferrules, collars, clamps and the like, which are also difficult to apply and are more expensive than the materials used in Clabburn. The construction of Lawrence et al. is somewhat simpler, but still requires placement of a mass of encapsulating particulate material. Furthermore, the splice shown in Lawrence et al. (as well as that shown in Clabburn) is not suitable for termination joints, i.e., a joint which effectively seals the end of the fluid-filled cable and allows a wide variety of cable accessories to then be attached thereto. It would, therefore, be desirable and advantageous to devise a transition joint for a fluid-filled cable which is simpler (and less expensive) to assemble than the foregoing splice assemblies, and which has wider application for connecting two of such cables together, for splicing one such cable to a plastic dielectric cable, for terminating the fluid-filled cable, or for receiving various other cable accessories.